Geochemical compositions of ore-related pyrite, quartz and fluid inclusions of Bangbu gold deposit in the Indus–Yurlung Zangbo suture zone, Tibet

Abstract

The Bangbu gold deposit is the largest Au deposit, and the only deposit in production, within an orogenic Au belt hosted by the Indus–Yurlung Zangbo suture zone in Tibet. Strontium isotopes, and in situ trace-element data from ore-related pyrite, quartz, and fluid inclusions were used to determine the composition of ore-forming fluids, the sources of ore components, and ore-forming processes. Arsenic, Se, and Ge are incorporated into Au-bearing pyrite by isomorphic substitution for S, while Co and Ni replace Fe in the pyrite lattice, and Au occurs either as lattice-bound or in the form of nanoparticles in pyrite. The individual fluid inclusions have Au contents of 0.59–4.41 ppm, with an average of 1.43 ppm. Single fluid inclusion analyses show a negative correlation between Au and Cl contents, indicating that Au did not complex with Cl ions and was probably transported as Au(HS)2−. Aluminum is positively correlated with Li and Ge in ore-related quartz, consistent with a contribution from magmatic hydrothermal fluids. The average 87Sr/86Sr ratio of fluid inclusions in quartz is 0.71577, which indicates a contribution from mantle-derived material. Gold is likely to have been sourced from fluids evolved from mantle-derived magma, rather than the surrounding rocks.